U.S. financier Warren Buffett, already one of his country's largest investors in clean technologies, says he's prepared to double his stake in renewable energy.

Speaking June 9 in Las Vegas, he noted that his investment company, Berkshire Hathaway (NYSE:BRK-B), already had invested about $15 billion in clean-energy enterprises, and added that he has "another $15 billion ready to go, as far as I'm concerned."

Earlier in his career, Buffett tended to invest in high-return businesses, but more recently he has said he likes the renewable energy industry because it's ripe for reinvestment and broader acquisitions. A prime example is an energy holding company in Iowa whose expansion Buffet funded in 2000.

That company, now known as Berkshire Hathaway Energy, runs electric grids in Britain, gas pipelines that cross the United States and electrical utilities in several U.S. states. And it keeps all its earnings, unlike many other energy companies, meaning it has on hand plenty of money – about $30 billion – to invest in the coming years.

"We're going to keep doing that as far as the eye can see," Buffett told the Edison Electric Institute's annual convention. "We'll just keep moving."

There's a growing need for investment in renewable energy, now that the U.S. Environmental Protection Agency has required utilities to cut carbon emissions by 30 percent by 2030 below the 2005 levels.

Nick Akins, the CEO of American Electric Power Co., told Bloomberg News that Buffett's words were "encouraging ... because as an industry we have a strong need for capital." Akins' company works with Berkshire on a project called Electric Transmission Texas, which operates power lines carrying electricity to customers from wind farms in the state.

In his Las Vegas address, Buffett seemed to be speaking casually. But Jeff Matthews, who has written books about Berkshire Hathaway, says no one should mistake the financier's intentions. Evidently, Matthews says, Buffet sees attractive returns on investment in renewables.